Molecular epidemiology of mycobacterium tuberculosis in the United Arab Emirates

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Abstract

Tuberculosis (TB) has re-emerged as a potential health threat in both developed and
developing countries. Notification rates in the United Arab Emirates (UAE) increased from
23 to 85 cases per 100,000 population between 1997 and 2003, an increase that has been
attributed to the presence of two Mycobacterium tuberculosis strains (Annual Statistical
Reports, 1998; Dissanayake et al., 2001; Annual Statistical Reports, 2003).
The principal aim of this study was to assess TB epidemiology in Al Ain, UAE, in
both UAE nationals and immigrants, using two genotypic methods: spoligotyping and
MIRU typing. A panel of 194 clinical isolates of M. tuberculosis complex was studied.
Eight global clades (CAS, Haarlem, LAM, EAI, Beijing, Africanum, T, X) and five
families were identified present in Al Ain. Strains were divided into principal genetic
groups by katG463/gyrA95 typing; group 1 was dominant. Two isolates were identified as
Mycobacterium kansasii by 16S rRNA sequence analysis. A high clustering rate of 46%
was detected by spoligotyping, compared to only 5.6% using MIRU typing, indicating a
low transmission rate. Identical MIRU profiles among two patients confirmed transmission
from an immigrant to a national.
The study revealed that tuberculin skin test detected more positive latent TB cases
(51%) among immigrants than nationals (21%); while results for the two groups for active
cases from chest radiography were comparable.
Although drug dispensing is not properly controlled, since patients can buy drugs
without prescription, this study showed that it has no direct effect on development of TB
drug resistance. Sequencing of rpoB showed the prevalence of rifampin resistance to be
low; only one isolate held a resistance mutation and another with a mutation unlinked to
resistance.
These findings identified Mycobacterium clonal structure and suggested the
exogenous nature of TB in Al Ain. Recommendations to improve the screening policy to
detect and treat both active and latent cases of TB among immigrants at arrival check points
have been made.